Copending application Ser. No. 07/562,289 teaches the preparation of adducts of epoxy resins and active hydrogen containing compounds, one or both of which contain one or more mesogenic moieties, as well as thermosettable compositions containing one or more of said adducts and products resulting from curing curable compositions thereof. In that invention, a plurality of active hydrogens (at least two or more) are required to be present in the active hydrogen containing compounds used to prepare the epoxy resin adducts. Thus, the active hydrogens of the active hydrogen containing compounds used in the preparation of the adducts, react, in part, with the epoxy groups of an epoxy resin also used in the preparation of the adducts and remain, in part, unreacted for future use as reactive moieties in a curable composition. When used to cure an epoxy resin, the mesogen-containing epoxy resin adducts of that invention provide cured products possessing substantial enhancement of physical and mechanical properties.
The present invention provides nitro (nitroso) group terminated adducts of epoxy resins prepared via reaction of an epoxy resin with a single active hydrogen containing compound which simultaneously contains one or more nitro (nitroso) groups. The resultant adducts of the present invention thus contain nitro (nitroso) terminating groups with no active hydrogen contributed by the single active hydrogen containing compound used to prepare said adduct. The advantages of the nitro terminated mesogen-containing adducts of the represent invention are multiple: A.) Reduction of the nitro groups provides a primary amine terminated adduct free of the chain extension (advancement) and/or branching potentially encountered if an aminophenol and an epoxy resin are reacted directly in an attempt to obtain the primary amine terminated adduct. B.) Reduction of the nitro groups provides exclusive primary amine termination in the adduct, whereas some extent of phenolic hydroxyl termination is likely if an aminophenol and an epoxy resin are reacted directly in an attempt to obtain the primary amine terminated adduct. Because of the higher reactivity of the amine group versus the phenolic hydroxyl group, the phenolic hydroxyl termination is, in fact favored under many conditions of reaction. If chain extension (advancement) through the primary amine group occurs (i.e., reaction of the primary amine hydrogens with two epoxide groups in separate epoxy resin molecules), a tertiary amine group becomes fixed in the adduct structure. C.) Functionalization of the backbone aliphatic hydroxyl groups, which result from epoxide ring opening by an active hydrogen containing compound to form an adduct, is very difficult in the presence of active hydrogen groups remaining in an adduct for future use as reactive moieties in a curable composition. By way of contrast, in the present invention, the nitro group terminated adducts with no active hydrogen contributed by the single active hydrogen containing compound used to prepare said adduct, may be functionalized through reaction of the backbone aliphatic hydroxyl groups without undesirable coreaction. The nitro groups present in the functionalized adduct are then reduced to provide primary amine termination for future use as reactive moieties in a curable composition. These amine terminated, functionalized adducts are preferred compositions of the present invention due to the liquid crystallinity often induced as a result of functionalization of the backbone aliphatic hydroxyl groups and improved processability resulting from lower melting temperatures.